Why are liverworts restricted to moist habitats

Another characteristic unique to liverworts is their lack of stomata, which are found in all other plants, including mosses and hornworts. In many species of liverworts, such as Marchantia , the one you will most likely see in lab, the antheridia and archegonia are not on top of the plant, but hanging down from the underside of odd little structures that look like tiny umbrellas. These umbrella-shaped structures are called the antheridiophore and archegoniophore.

The bi-flagellated sperm swims to the egg, and fertilization takes place to form a diploid 2N zygote. The tiny diploid sporophytes, which remain attrached to the parent plant, have a very simple structure. Meiosis within the sporophyte produces a number of haploid spores. These spores are surrounded by curious long and twisted moist cells called elaters.

When the capsule dries and bursts, the elaters twist and jerk around in a way that scatters the spores in all directions. Liverworts can also reproduce asexually by means of special structures called gemmae cups.

These little cups can be easily seen on the surface of the plant. Each gemma cup contains a number of tiny plantlets called gemmae, and a single drop of water will disperse them. The green gametophytes of the hornwort look very much like a liverwort. But their small sporophytes more closely resemble those of mosses.

The sporophytes grow out of the gametophyte, and look like a little upright horn. Like mosses, hornworts have stomata, and so are probably more closely related to mosses and other plants than to the liverworts they mat resemble. These plants are symbiotic with the cyanobacteria Nostoc.

The cyanobacteria fixes nitrogen for the hornwort. Division Hepaticophyta - liverworts Marchantia, Conocephalum, Porella; fr. Examine the living mosses on display.

Notice the small capsules on top of the tiny sporophytes. Mosses generally grow in one of two growth types: cushiony moss and feathery moss. Examine slides of the antheridia and archegonia. The sausage shaped antheridia produce sperm, and the flask shaped archegonia produces eggs.

Examine slides of the protonema. What type of algae does it remind you of? This resemblance is additional evidence that green algae gave rise to all higher plants.

Examine the terrestrial liverworts Marchantia and Conencephalum one or both should be on display. How does their growth habit differ from that of the mosses? Can you see any gemmae cups on the upper surface of these plants?

Examine the aquatic liverworts like Porella and Riccia one or both should be on display. Notice how they differ from the more terrestrial forms of liverwort. Look at the preserved liverworts , and observe their distinct reproductive structures they look like little green umbrellas.

How does their life cycle differ from mosses? Hint: Be sure you understand the general life cycle of plants, and can tell which stages are haploid gametophytes 1N or diploid sporophytes 2N. We'll learn several life cycles in lecture and in lab moss, fern, pine, flowering plant , but all of them are variations on the same basic theme.

Just as the evolution of spores was the key to the invasion of the land surface by bryophytes, the invention of complex vascular tissues let tracheophytes complete the conquest of dry land. There are about , species of vascular plants, grouped in nine divisions. Tracheophytes all have a well developed root-shoot system, with highly specialized roots, stems, and leaves, and specialized vascular tissue xylem and phloem that function like miniature tubes to conduct food, water, and nutrients throughout the plant.

Because ferns and fern allies posses true vascular tissues, they can grow to be much larger and thicker than the bryophytes. The ferns and fern allies non-seed tracheophytes mark two major evolutionary strides. In these and in all more advanced plants, the leafy green diploid sporophyte now becomes the dominant stage. The tiny gametophyte may be either autotropophic like the fern prothallus or heterotrophic like the gametophytes of some lycopsids , and is generally free living and independent of the parental sporophyte.

Unlike the vascular sporophytes, the gametophytes have no vascular tissue at all. These gametophytes are therefore very small, and develop best in moist areas, where they can absorb water directly from their surroundings. Like the bryophytes, ferns and fern allies are still restricted to moist habitats. Their flagellated sperm need a thin film of water to swim between the antheridium and the archegonium. And when the baby sporophyte grows up from the gametophyte, it is exposed to desiccation drying up.

This basic strategy of a free-swimming sperm and a non-motile egg is shared by plants, animals, and algae. It makes sense, because it means only one set of gametes has to make the perilous journey outside of the organism. The ferns and fern allies germinate from spores. These plants are mostly homosporous - their spores are identical and you can't differentiate which will grow into male or female plants. They are also monoecious - both the archegonia and antheridia male and female reproductive structures are borne on the same plant.

Contrast these primitive vascular plants with the more advanced seed plants, the gymnosperms and angiosperms, which germinate from seeds rather than from spores. Seed plants are all heterosporous. It is easy to differentiate the larger female megaspore from the smaller male microspore. The sperm of seed plants have no flagella.

They lack antheridia, and only a few still have an archegonia. Unlike the more primitive ferns and fern allies, seed plants are mostly dioecious , having separate male and female plants. In many of these primitive plants, certain leaves are specialized for reproduction. These modified leaves, or sporophylls , bear the sporangia at their bases. These sporophylls usually branch out from a shortened stem, forming a club shaped structure called a strobilus.

The pine cone and the flower are elaborate variations on these primitive strobili. There are four divisions of non-seed tracheophytes, vascular plants that reproduce by means of spores , the Psilophyta, Lycophyta, Sphenophyta, and Pterophyta. Before these non-seed tracheophytes evolved, the bryophytes were the dominant form of plant life. The evolutionary edge of having a more efficient conducting system, and a well-developed root-shoot system enabled them to outcompete bryophytes.

There are only two living genera of whisk ferns, sole survivors of a large and widespread group of early land plants. In addition to the living Division Psilophyta, the psilopsids, there are two extinct divisions of primeval vascular plants. The primitive whisk ferns resemble these extinct pioneers in many ways. They are the only living vascular plants that lack a root-shoot system, a characteristic they share with both extinct Divisions of ancestral vascular plants.

Some recent molecular evidence suggests that one, or even both, of the living genera of psilopsids may actually be more closely related to ferns, like a fern that has reverted to more primitive traits. If this is true, then Psilophyta will join the ranks of the numerous extinct Divisions of plants. Psilopsids are found in tropical and subtropical areas, and occurs throughout the southern US.

I once found one growing on my back porch under the leaves of a spider plant. Whisk ferns are a common weed in greenhouses all over the world. They are simple green upright stems, with dichotomous branching. They have no leaves, and no true roots.

The outer tissues of the stem do all the photosynthesizing. A portion of the stem called a rhizome runs along the ground, or just below it. A rhizome is a horizontal stem that spreads the plant around. Roots grow out the bottom of the rhizome, and a new plant can arise at the same point from the top.

The green stem-like plant is the diploid sporophyte, the dominant stage in the life cycle. In the small sporangia bright yellow that form along the upper stems, the spore mother cell forms haploid spores by meiosis. Their gametophytes are tiny little thread-like underground plants that lack chlorophyll, and live as heterotrophs in the soil, looking and acting much like a tiny fungi.

It actually contains a symbiotic fungi, the same mycorrhizae that live in the rhizomes of the adult sporophyte. Division Lycophyta - 1, sp. Their are only five living genera of lycopsids, but at one time from the distant Devonian, about mya, well into the Carboniferous, they were the dominant form of vegetation on the face of the Earth. Now they are reduced to a shadow of their glorious past, inconspicuous little plants in the forest understory. The tropical species are small epiphytes plants that grow on other plants.

Their roots grow from special underground stems called rhizomes, as do most of these primitive tracheophytes. In some species the sporophylls are mixed in with the scale-like leaves. The sperm swim down the strobilus to the archegonia, and the zygote that forms is retained in the cone, which ripens and falls to the ground.

The gametophytes are independent and free-living, They are curious creatures that look and act nothing like their sporophyte parents. They can be either heterotrophic or autotrophic, and usually have a symbiotic fungi associated with them. Many of the lycopsids are heterosporous. Selaginella is a good example of a heterosporous plant. Division Sphenophyta - 15 sp. In waste places, disturbed areas like trails and railroad beds, and in odd corners of fields and forests you might find another small plant quietly dreaming of its former splendor, the horsetail.

Horsetails appeared in the late Devonian, and were among the dominant forest trees for hundreds of millions of years. Only one genus of Sphenophyta still exists, the genus Equisetum , and it may be the oldest living genus of plants on earth. Horsetails towered among the Carboniferous forests, reaching heights of feet.

Much of the coal deposits we exploit for fuel today were formed from horsetails and other trees during the Carboniferous, toward the end of the Paleozoic. Horsetails have true roots, stems, and leaves, though the leaves are little more than flattened stems.

Their hollow, ribbed stems are jointed, kind of like a stalk of bamboo, and a whorl of leaves arises at each joint. The plants are spread vegetatively by rhizomes. The stems feel very rough, because the epidermal tissues are impregnated with tiny grains of silica sand. This probably helps protect the plant against herbivores. The green plant we see is the diploid sporophyte generation. The stalks can be highly branched vegetative stalks, which actually look like horse tails, or straight unbranched reproductive stalks, which are tipped with a large strobilus containing the sporangia.

The homosporous spores develop into a teeny-tiny green gametophyte, just a few mm long, that looks like the gametophyte of a fern. The gametophyte is haploid, free-living, and autotrophic. Ferns probably evolved from the psilopsids, sometime in the Devonian, relatively early on in land plant evolution.

The most abundant mosses in Arches can remain dry for years, and will rehydrate in seconds after contact with water. Some species begin photosynthesizing less than one hour after being moistened. There is no complete inventory of mosses and liverworts in Arches. At least 20 moss species are known to colonize biological soil crusts, with Syntrichia caninervis being the most common.

Grimmia orbicularis accounts for 80 percent of the moss found on rock surfaces. Like all photosynthetic organisms, mosses are primary producers that build biomass through photosynthesis. They enrich ecosystems with organic matter, forming the basis of the food chain. As a component of biological soil crusts, mosses trap airborne soil particles, reduce erosion, retain water and may enhance water infiltration. Explore This Park. Arches National Park Utah. Info Alerts Maps Calendar Reserve.